Health effects of chlorpyrifos

Introduction

Chlorpyrifos is an organophosphorus insecticide that has been widely used in the home and on the farm. In the home, chlorpyrifos has been used to control cockroaches, fleas, and termites; it has also been an active ingredient in some pet flea and tick collars. On the farm, it is used to control ticks on cattle and as a spray to control crop pests. In 1997, chlorpyrifos was voluntarily withdrawn from most indoor and pet uses by the manufacturer, DowElanco.

Chlorpyrifos is a white crystal-like solid with a strong odor. It does not mix well with water, so it is usually mixed with oily liquids before it is applied to crops or animals. It may also be applied to crops in a microencapsulated form. Chlorpyrifos is the active ingredient of various commercial insecticides including Dursban® and Lorsban®.

Pathways for chlorpyrifos in the environment

Chlorpyrifos enters the environment through direct application to crops, lawns, domesticated animals, and in the home and workplace. Chlorpyrifos may also enter the environment through volatilization, spills, and the disposal of chlorpyrifos waste.

Chlorpyrifos that has been applied to the soil generally stays in the area where it has been applied because it sticks tightly to soil particles. Because of this, there is a low chance that chlorpyrifos will be washed off the soil and enter local water systems. Also, since it does not mix well with water, if it does get into the natural waters, it will be in small amounts and will remain on or near the surface and will evaporate. Volatilization is the major way in which chlorpyrifos disperses after it has been applied. Once in the environment (soil, air, or water), chlorpyrifos is broken down by sunlight, bacteria, or other chemical processes.

Exposure to chlorpyrifos

You can be exposed to chlorpyrifos in many places because of its wide range of uses. You can be exposed to it in your home or office if chlorpyrifos has recently been used to control household pests such as fleas or cockroaches. Exposure can also occur outside your home if chlorpyrifos has been applied to the ground around the foundation to control termites. Chlorpyrifos degrades rapidly in the environment; however, low levels may persist for long periods of time after it has been applied either inside or outside the home. Opening windows before and after chlorpyrifos spraying rapidly lowers airborne levels in a house.

You can also be exposed to chlorpyrifos in a farm setting. The greatest risk occurs soon after a crop has been sprayed, because that is when its levels will be the highest. However, chlorpyrifos rapidly degrades and becomes bound to plants and the ground. The EPA recommends a 24-hour waiting period before entering fields where chlorpyrifos has been applied. In addition, there is the risk of exposure to chlorpyrifos when it is being prepared for use. Care should be taken to ensure that only a licensed applicator sprays chlorpyrifos, and that unnecessary or unprotected individuals remain away from the site of application during the spraying.

Chlorpyrifos can also be found at some waste disposal sites, so exposure to higher levels than what is commonly found after home or commercial use may occur there.

Pathways for chlorpyrifos in the body

You can be exposed to chlorpyrifos in many places because of its wide range of uses. You can be exposed to it in your home or office if chlorpyrifos has recently been used to control household pests such as fleas or cockroaches. Exposure can also occur outside your home if chlorpyrifos has been applied to the ground around the foundation to control termites. Chlorpyrifos degrades rapidly in the environment; however, low levels may persist for long periods of time after it has been applied either inside or outside the home. Opening windows before and after chlorpyrifos spraying rapidly lowers airborne levels in a house.

You can also be exposed to chlorpyrifos in a farm setting. The greatest risk occurs soon after a crop has been sprayed, because that is when its levels will be the highest. However, chlorpyrifos rapidly degrades and becomes bound to plants and the ground. The EPA recommends a 24-hour waiting period before entering fields where chlorpyrifos has been applied. In addition, there is the risk of exposure to chlorpyrifos when it is being prepared for use. Care should be taken to ensure that only a licensed applicator sprays chlorpyrifos, and that unnecessary or unprotected individuals remain away from the site of application during the spraying.

Chlorpyrifos can also be found at some waste disposal sites, so exposure to higher levels than what is commonly found after home or commercial use may occur there.

Health effects of chlorpyrifos

To protect the public from the harmful effects of toxic chemicals and to find ways to treat people who have been harmed, scientists use many tests.

You should know that one way to learn whether a chemical will harm people is to determine how the body absorbs, uses, and releases the chemical. For some chemicals, animal testing may be necessary. Animal testing may also help identify such health effects as cancer or birth defects. Without laboratory animals, scientists would lose a basic method for getting information needed to make wise decisions that protect public health. Scientists have the responsibility to treat research animals with care and compassion. Scientists must comply with strict animal care guidelines because laws today protect the welfare of research animals.

Additionally, there are vigorous national and international efforts to develop alternatives to animal testing. The efforts focus on both in vitro and in silico approaches and methods. For example, the National Toxicology Program (NTP) at the National Institute of Environmental Health Sciences (NIEHS) created the NTP Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM) in 1998. The role of NICEATM is to serve the needs of high quality, credible science by facilitating development and validation—and regulatory and public acceptance—of innovative, revised test methods that reduce, refine, and replace the use of animals in testing while strengthening protection of human health, animal health and welfare, and the environment. In Europe, similar efforts at developing alternatives to animal based testing are taking place under the aegis of the European Centre for the Validation of Alternative Methods (ECVAM).

In people, short-term oral exposure (one day) to low (milligrams) levels of chlorpyrifos can cause dizziness, fatigue, runny nose or eyes, salivation, nausea, intestinal discomfort, sweating, and changes in heart rate. Short-term oral exposure to much higher (grams) levels of chlorpyrifos may cause paralysis, seizures, loss of consciousness, and death. Reports in people also show that short-term exposure to chlorpyrifos may cause muscle weakness weeks after the original symptoms have disappeared. Other effects of exposure to chlorpyrifos include changes in behavior or sleeping pattern, mood changes, and effects on the nerves and/or muscles in the limbs (which may appear as odd sensations such as numbness or tingling, or as muscle weakness). The EPA has not classified chlorpyrifos for carcinogenicity (Class D).

Medical tests for exposure to chlorpyrifos

There is a general test that can be performed to determine if you have been exposed to carbamate or organophosphate insecticides. Those types of pesticides inhibit the activity of acetylcholinesterase, the enzyme responsible for inactivating acetylcholine, the compound ultimately responsible for most of the toxic symptoms seen with chlorpyrifos. The test measures the activity of the enzyme acetylcholinesterase in the blood or a similar enzyme, pseudocholinesterase, in the plasma, or both. If enzyme activity is inhibited, then exposure to an organophosphate or carbamate pesticide is suspected. There is also a biochemical test that can determine if you have been specifically exposed to chlorpyrifos. After chlorpyrifos enters the body, it is changed by the liver into other forms of the compound that may or may not be less toxic than the original material. The major nontoxic chlorpyrifos metabolic product formed by the liver is 3,5,6-trichloro-2-pyridinol, or TCP. TCP is primarily eliminated from the body in the urine and can be detected in the urine using readily available laboratory equipment. The extent of the exposure, length of time after exposure, and the amount of water in the body will affect the level of TCP in the urine. Typically, TCP can be found in the urine for several days after exposure to chlorpyrifos. In addition to chlorpyrifos, TCP is a metabolite of methyl chlorpyrifos and triclopyr. TCP may also be found in the environment, but it is unlikely that urinary levels of TCP result from environmental-TCP exposure. Direct exposure to chlorpyrifos or chlorpyrifos-like compounds is the most likely cause.

Further Reading

Disclaimer: This article is taken wholly from, or contains information that was originally published by, the Agency for Toxic Substances and Disease Registry. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the Agency for Toxic Substances and Disease Registry should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.

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Citation

(2008). Health effects of chlorpyrifos. Retrieved from http://www.eoearth.org/view/article/51cbedfa7896bb431f695383

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